The present invention relates to well rigs such as drilling rigs and service rigs, and particularly to a hydraulic energy-storing well rig lift system, wherein a high pressure energy-storing system and a composite cylinder or a cylinder group are used to carry out the lifting operation and to recover the potential energy of pipe string released during the lowering operation.
At present, oil well rigs lift system (service rigs and drilling rigs lift system) are very much the same. Most of them comprise power machines, driving devices, gear boxes, derricks, crown blocks, travelling blocks, and draw works. In the operation of the well rigs, tubings or drill pipes up to tens of hundreds of tons and with length up to thousands of meters are lifted up and laid down once and again and a large amount of fuel is consumed.
During the lifting operation, when a pipe or pipe-stand is lifted, the actual lifting time takes only 1/3-1/4 of the whole process, and the rest is for some auxiliary operations such as unloading a single pipe, placing the unloaded pipes to a proper position, etc. However, during the lifting operation, a great deal of work is done in a short duration, and therefore the installed capacity of the well rig power machine must be large enough to meet the demand for lifting. And a power machine with large installed capacity will consume a large amount of fuel even during idling or near idling in the auxiliary operations.
During the lowering operation, although the descending of the pipe string will release a large amount of potential energy, the power machine cannot stop running and still consumes a lot of fuel. And not only the released potential energy of pipe string is unable to be recovered for use but it is also necessary to control the lowering operation by means of braking and other methods which consume large energy, otherwise an accident may occur.
The hydraulic technique now is very popular in well rigs. Hydraulic elements and apparatuses, such as cylinders, valves, pumps, oil tanks and compensators, etc., are widely employed in various rigs, drills and drifters for controlling, tool feeding, load indicating and for compensating purposes.
Although hydraulic systems employed in many kinds of drilling tools are known, it is not known how to store the energy of a power machine or how to store the potential energy of the pipe string released during lowering operation, and how to reuse the stored-energy as desired, which are essential matters of the present invention. For instance, U.S. Pat. No. 3,986,564 issued to Bender on Oct. 19, 1976, discloses a hydraulic well rig utilizing hudraulic cylinders to carry out the lifting operations so as to eliminate winches, driving devices and crown blocks, but the above-mentioned energy storage method is not taught in this Patent.